Multicapillary monolith

ABSTRACT

The invention relates to a monolithic porous material made of amorphous silica or activated alumina, comprising substantially rectilinear capillary channels that are parallel to one another, wherein: 
     the channels have a substantially uniform cross-section relative to each other, 
     the cross-section of each channel is regular over its entire length, 
     the channels pass through the material from end to end, 
     the length of the channels is equal to or more than 10 mm. 
     The invention also relates to an annular, radial or axial chromatographic apparatus, the packing of which consists of at least one said monolithic material. 
     The invention also relates to processes for manufacturing such a monolithic material.

FIELD OF THE INVENTION

The present invention concerns a monolithic porous material of amorphoussilica or activated alumina, comprising substantially rectilinearcapillary channels that are parallel to one another, passing through thematerial from end to end and intended in particular for use inchromatography.

BACKGROUND OF THE INVENTION

The close contact between two phases such as a gas and a liquid topromote their chemical or physical interaction is an important operationin chemical engineering.

To promote interface phenomena on the contact surface between these twophases, it is endeavoured to increase this contact surface as much aspossible, and to increase the effects of mixing in the vicinity thereof.

For such purpose, beds of fine solid particles are frequently usedthrough which a fluid passes and with which they interact.

These beds, called particle beds or packings, offer large exchangesurfaces on account of the small size of their constituent particles,and on account of the large divided status of the fluid passing throughthem.

These phenomena promote the speedy accomplishing of material transferprocesses, chemical reactions or any other diffusion-related phenomena.

Their applications particularly cover the fields of both analytical andpreparative liquid and gas chromatography.

U.S. Pat. No. 4,657,742 to Beaver P. proposes an alternative to theseparticle packings comprising a tube packed with aligned fibres which maybe porous and hollow. One disadvantage of this packing is that theeluting fluid flows both inside and outside the hollow fibres in thevoids left between their stacking. Since the eluting fluid flows at twovery different rates inside the hollow fibres and on periphery thereofin the interstices separating the fibres of circular section, there isresulting loss of efficacy. Another disadvantage of this device is thatthe walls of the hollow fibres must be sufficiently thick so that theycan be handled and packed withstanding the mechanical stresses inducedby the stacking thereof. This means that the diffusional balancingbetween adjacent fibres is slow, and the packing is little efficient.Another disadvantage of this device is that it is difficult to apply tobundles of fibres of large diameter since the chemical stability of thepacking would be difficult to ensure.

U.S. Pat. No. 4,957,620 to Cussler E. describes the use of bundles ofhollow polymer fibres for use as chromatographic column. The assemblysuffers from the same disadvantages as above: the thickness of the wallof the fibres must be higher than that of the central channel in orderto impart sufficient mechanical strength to these fibres allowing thehandling and assembly thereof. As a result, transfers of material bydiffusion between the material of the walls and eluting fluent are slow.The eluting fluid flows at two very different rates inside the hollowfibres and on the periphery thereof. Here again the stabilization oflarge diameter packing is difficult owing to the lack of strong bondsbetween adjacent fibbers.

U.S. Pat. No. 4,818,264 describes the use of bundles of capillarycolumns in glass or silica to perform multicapillary gas chromatography.This system has the serious drawback that the capillaries behaveindependently of each other. On this account, it is difficult to obtainidentical behaviour of the different channels and careful, scrupulousattention must be given to the manufacture of channels that are allidentical.

Patent application US 2005/0139536 to Belov Y. P. describes achromatographic column whose channels are coated with differentthicknesses of stationary phase so as to offset hydrodynamicinequalities between the different channels. This work exemplifies thedifficulty in obtaining good performance levels with a multicapillarycolumn formed of individualized channels which do not communicate bydiffusion.

The publications by Nishihara H. <<Ordered macroporous silica by icetemplating>>, Chemistry of Materials, 28 Feb. 2005, pages 683-689 andMukai S. R. <<Formation of monolithic silica gel microhoneycomb (SMH's)using pseudo steady state growth of microstructural ice crystals>>Chemical Communications, 4 Mar. 2004, pages 874-875 describe a potentialpathway for forming multicapillary structures in silica. The documentsrefer to a method of manufacturing microstructures of ordered poroussilica, of honeycomb shape and 3.6 to 40 μm in diameter. The methodcomprises causing directional growth of ice crystals in low-cohesionsilica gels and evaporating a solvent by freeze-drying.

However, the described method only functions with silica gels having lowcohesion i.e. with low silica concentration. The structures obtained aretherefore very lightweight, namely having a density of the order of 0.12g/cm³ according to the authors of these publications. The relativevolume of the capillaries is high. As such, they will not perform wellin liquid chromatography for which a dense packing is sought havingstrong retention capacity. In addition, packing that is so lightweightis mechanically fragile.

Additionally, examination of all the photographs in the two articlesshows that the diameters of the channels differ by a factor of about 10,and that these channel diameters fluctuate to a large extent and areirregular over their length. These channels have most variableenvironment and morphology, their cross-section possibly being square,pentagonal, hexagonal, etc. These irregularities mean that such packingis inefficient for high performance analytical chromatography for whichperfect homogeneity of the packing is required.

Finally, the packings described in these articles are obtained over arestricted range of diameters, from 3.6 to 42 μm. Yet, the rangeextending below 2 μm is of particular interest for application in highpressure liquid chromatography (HPLC), and the range extending above 50μm is of particular interest for application to gas chromatography.

U.S. Pat. No. 6,210,570 to Holloway R. describes monolithic packing inporous silica for chromatography. Said packing is formed of more or lessspherical pores forming tortuous passages through the packing. Thesepassages are tortuous and a fluid passing them encounters numerousobstacles, the pores and the solid being randomly distributed in spacewithin the packing. This forms a major difference with a flow through anempty capillary tube in which the fluid does not encounter anymicroscopic obstacle over an optimal rectilinear pathway. They display alower pressure drop than a particle packing but higher than that of acapillary having the same separation efficacy for a given analysis, andhave intermediate separation impedance between the two. They have theadvantage of allowing a macroscopically uniform flow of the elutingfluid through the packing on account of their monolithic structure,unlike the case with the stack of capillary tubes described in patentU.S. Pat. No. 4,657,742.

The following publications: N, Ishizuka, Designing monolithic doublepore silica for high speed liquid chromatography, Journal ofChromatography A, 797 (1998), 133-137, K Nakanishi, Phase separation insilica sol-gel system containing polyacrylic acid, Journal of noncrystalline Solids 139 (1992, 1-13 and 14-24, K. Nakanishi, Phaseseparation in Gelling Silica-Organic Polymer Solution: SystemsContaining Poly(sodium styrenesulfonate), J. Am. Ceram. Soc. 74 (10)2518-2530-30 (1991) deal with the same subject matter as the Hollowaypatent. The aim is to obtain a monolithic packing in silica comprisingtwo families of pores, one of interconnected macropores in which aliquid is able to flow relatively freely and the other a family ofmesopores or micropores creating a specific surface area and henceactivity for the exchange of material.

However, the large majority of separations are still conducted onparticle beds, which are easier to manufacture.

There is therefore a need for a product having advantages in terms ofreliability and ease of manufacture of particle packing, allowing theuniform microscopic and macroscopic flow of eluting fluid in the bed,whilst maintaining the advantages of capillary columns.

BRIEF DESCRIPTION OF THE INVENTION

For this purpose, the invention proposes a monolithic porous materialbased on amorphous silica or activated alumina, comprising substantiallyrectilinear capillary channels parallel to one another, characterized inthat:

-   the channels have a substantially uniform cross-section in relation    to one another,-   the cross-section of each channel is regular over the entire length    thereof,-   the channels pass through the material from end to end.

Advantageously, the length of the channels is equal to or greater than10 mm, preferably greater than 20 mm and further preferably greater than50 mm.

By <<based on>> is meant that the structure of the monolith isessentially formed of amorphous silica or activated alumina, optionallysurface-modified.

By <<substantially uniform cross-section>> is meant herein that thediameters of the different channels are close to each other i.e. inparticular that the mean diameter of one channel does not on averagediffer by more than 30% from the average of the diameters of thechannels.

The standard deviation of the diameter of the channels is less than 30%from the mean, preferably less than 5%.

By <<regular cross-section>> is meant that the channels respectivelyhave a substantially constant cross-section over their entire length,i.e. the diameter of a channel does not vary by a factor of more than 2between the narrowest regions and the widest regions.

The material advantageously has a density of more than 0.12 kg/litre.

In particularly advantageous manner, the material has a relative volumeof the capillary channels that is less than 90%.

The thickness of the wall between two adjacent channels, in itsnarrowest part, is advantageously less than one half of their diameter.

According to one embodiment of the invention, the capillary channelshave a diameter of between 0.1 and 1.5 micrometres.

According to another embodiment of the invention, the capillary channelshave a characteristic diameter or cross dimension of more than 50 μm.

The material is advantageously formed of amorphous silica, which may ormay not be silane-modified on the surface, or of an alumina γ, χ, κ, ηor θ which may or may not be surface modified.

The monolithic material advantageously has an elongate shapecharacterized by a length (i.e. the length of the capillary channels)greater than its dimension in a direction perpendicular to the channels.

A further subject of the invention is a chromatographic column whosepacking comprises at least one monolithic porous material such asdescribed above.

Advantageously, the monolith is sufficiently long so that a singlemonolith is sufficient for application in chromatography.

Optionally, several monoliths can be stacked.

A further subject of the invention is an axial, continuous annularchromatographic instrument in which the packing comprises at least onemonolithic porous material such as described above.

A further subject of the invention is a radial, continuous annularchromatographic instrument in which the packing comprises at least onemonolithic porous material such as described above.

The invention also concerns a process for manufacturing a monolithicporous material in amorphous silica or activated alumina comprisingsubstantially rectilinear capillary channels parallel to one another,characterized in that it comprises the steps of:

-   providing a bundle of so-called precursor fibres of the channels    whose diameter is equal to the diameter of the capillary channels,-   forming a porous matrix of amorphous silica or activated alumina    around the fibres,-   eliminating the fibres so as to form said capillary channels in said    matrix.

Optionally, the precursor fibres of the channels comprise an ablativelayer of coating material which is eliminated at a first treatment stepfor fibre removal.

According to one particular embodiment of the invention, the precursorfibres of the channels optionally comprising their coating of ablativematerial are coated with a spacer before forming the bundle so as toensure a minimum thickness of monolith between two

adjacent channels. According to one embodiment of this method, thefibres are formed of a hydrolysable polymer, the fibres are assembled ina bundle, the bundle is immersed in a silica gel precursor solution,this solution being caused to gel around the fibres, and the fibres areremoved by hydrolysis to soluble species of low molecular weight.

By <<silica gel precursor solution>> is meant a liquid whose compositionis such that as it develops under the conditions of the manufacturingprocess, it leads to a silica gel.

According to another embodiment of this method, the channel precursorfibres are of wire fibre with low melting point coated with a film ofsilica or activated alumina, assembled into a bundle, the bundle isimmersed in a silica gel or activated alumina precursor solution, thissolution being caused to gel around the fibres and the fibres areeliminated by melting and draining the molten liquid outside thematerial.

If the material is amorphous silica, this amorphous silica can bereinforced by depositing silica on the surface of its constituentparticles before it is dried.

According to one embodiment of this process, the porous matrix ofamorphous silica has a high proportion (i.e. preferably higher than 40%)of macropores allowing the circulation of a fluid within the monolith.

Alternatively, the invention proposes a process for fabricating amonolithic porous material of amorphous silica comprising substantiallyrectilinear capillary channels that are parallel to one another,comprising the steps of:

-   forming channels in at least one sheet of a silicone elastomer,-   stacking or rolling this or these sheets so as to form conduits    which will form capillary channels,-   pyrolysis and oxidation of the silicone to amorphous silica.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeapparent from the following detailed description with reference to theappended drawings in which:

FIG. 1 is a cross-sectional view of a cylindrical multicapillary packingfor chromatography according to the invention, following a directionperpendicular to its major axis;

FIG. 2 is an overhead view of one side of the cylindrical packing inFIG. 1;

FIG. 3 is a cross-sectional view of a film of silicone elastomer whereinchannels are etched which, after stacking or rolling, are intended toform the capillary channels;

FIGS. 4, 5 and 6 are block diagrams of a continuous annularchromatograph using multicapillary packing according to the invention;

FIGS. 7 and 8 are block diagrams of a radial multicapillary packing forradial annular chromatograph;

FIG. 9 is a photograph of a cut made through a monolithic porousmaterial prepared according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention allows a structure to be obtained that is capable ofcompeting with particle packing, in the diversity of applicationsthereof and in particular in chromatography.

The monolithic material is a solid (amorphous silica or activatedalumina) that is essentially porous and comprising a multiplicity ofrectilinear, contiguous channels that are parallel to one another, whichare channels of capillary dimensions i.e. a diameter not exceeding a fewmillimetres) and which impose a preferable direction for the fluid inthe bed. The porous mass offers a large exchange surface between thefluid and the solid, which may be an adsorbent or the medium of astationary phase.

The porous nature of the solid allows exchange of material by diffusionbetween the adjacent channels, therefore allowing concentrationgradients to be reduced between neighbouring capillary channels and areduction in their irregularities.

These irregularities are due to small differences in terms of topologyand diameter between the different channels.

The monolithic structure of the packing obtained also allows the ensuredtransiting of the entirety of the fluid through the core of the channelswithout any other possible pathway, and the ensured mechanical cohesionof the packing.

A monolith can be defined as follows: a structure having a multiplicityof channels of capillary dimensions operating in parallel crossingthrough a mechanically cohesive mass of porous material from end to end.

The monolith may be of any suitable length for the process to be carriedout, between a few millimetres and several metres.

The monolith may have a cross-section that is suitable for the processto be carried out, between a few square micrometres and several squaremetres.

Two main mineral oxides are known for achieving chromatographicseparations: amorphous silica and activated alumina. The first is asilicon oxide, and the second is an aluminium oxide. These two oxideshave numerous points in common, in particular:

-   -   they can be obtained in the form of solids with high specific        surface area, several hundred m² per gram;    -   they can be shaped using the sol-gel route;    -   they have a very active surface for the adsorption of organic        molecules, making them selective for a chromatographic        separation process.

The packing materials of the invention are therefore preferably composedof amorphous silica or activated alumina.

According to the invention, the cross-sections of these channels areregular and uniform i.e. the channels respectively have a substantiallyconstant cross-section over their entire length and diameters of closesize.

By regular or substantially constant cross-section is particularly meanta diameter which does not vary by a factor of more than 2 between thenarrowest regions and the widest regions of one same channel.

By diameters of close size is particularly meant that the mean diameterof a channel does not on average differ by more than 30% from theaverage of the diameters of the channels.

In other words, and if it is assumed that the diameters of the channelsare distributed according to a reduced centred normal law, the standarddeviation must preferably not exceed 30%. Preferably, this standarddeviation does not exceed 5% and further preferably 0.5%.

Preferably the channels have a constant and uniform arrangement andshape.

According to one preferred embodiment of the capillary channels, thechannels preferably have a substantially circular cross-section.

However, the channels may assume different geometric shapes, inaccordance with the method of manufacture of the fibres used forfabrication thereof. These geometric shapes may be a circle, a square, apolygon with substantially equal sides. The diameter of the channel inthis case is the diameter of the circle inscribed within this geometricshape.

According to one preferred embodiment of the invention, themulticapillary packing contains a high proportion of solid.

A high volume proportion of a solid with a high specific surface areaincreases packing capacity and requires a smaller volume of bed.

In particular, this proportion is such that its density is greater than0.12 kg/litre and is preferably greater than 0.15 kg/litre.

In even further relevant manner, these packing materials are defined bythe proportion of volume occupied by the capillary channels in themonolith. In this text, this ratio will be called the <<relative volumeof the capillaries>>.

Preferably the relative volume of the capillaries is less than 90%, morepreferably less than 80% for analytical applications. For preparativechromatography applications, the relative volume of the capillaries maybe much lower, preferably but not limited thereto less than 40%, morepreferably less than 20%, so as to increase the packing capacity to amaximum.

Preferably, the wall separating the adjacent parallel channels at itsnarrowest point has a thickness less than one half of their diameter orof their characteristic transverse dimension.

Preferably, the walls separating the channels are regular in dimensionand in arrangement.

Preferably, for absorption processes, the gel forming the monolithcomprises a high volume of mesopores of diameter 4 nm to 25 nm, so as tocreate a specific surface accessible by diffusion.

The porous volume measured, excluding the volume of the channels, mayfor example be between 0.3 and 3 cm³/g for silica and between 0.2 and0.5 cm³/g for alumina.

For silica, if bimodal gels are used such as those described in theHolloway patent and in the publication by N, Ishizuka, the porous volumemay be notably higher when including the macropores.

Preferably, for absorption processes the gel forming the monolith has ahigh specific surface area, of between 90 m²/g and 600 m²/g for example,for silica and alumina.

Preferably, for implementation of the invention, the monolith has a highnumber of channels, for example more than five, preferably more thanfifty, further preferably more than five hundred.

It is noted that the pressure drop in a multicapillary packing is of oneor two orders of magnitude smaller than in a bed of particles of samecharacteristic dimension. This results from expression of the laws ofDarcy and Poiseuille.

Therefore, the separation impedance of a multicapillary packing inchromatographic separation may be increased by one or two orders ofmagnitude compared with a particle packing.

The multicapillary packing comprises a large number of capillaries ofequal length and mean radius R. It is considered that the diameterstatistically follows a normal law with a standard deviation σ_(R). Itcan be calculated that for this multicapillary packing the maximumnumber of theoretical plates of chromatographic separation which can beobtained is written:

N _(R,max) =R ²(9·σ_(R) ²)

For example, if the relative standard deviation is 1 ‰, the maximumnumber of plates of the separation will be 1.1 10⁵. If this diameter hasa relative standard deviation of 1%, 1100 plates are already availablewhich is sufficient for numerous chromatographic separations.

The results can in fact be improved if the channels are not perfectlyindividualized but are closely stacked or close to each other withsufficiently thin walls separating them such that the transfer ofmaterial takes place between each channel and its closest neighbours.

This can be achieved by fabricating the multicapillary packing in apartly or fully porous mass allowing each channel to equilibrate withits neighbours via diffusion. The resulting effect, whose calculationdepends on the spatial arrangement of the capillaries, will be anattenuation or damping of the difference in behaviour of the individualchannels, owing to transfers of diffusive material from one channel toanother.

The observed resulting effect is an increase in efficacy, the randomvariations in the diameters of the channels being averaged out by thediffusion process.

According to another advantage of the invention, the porous mass is themedium of a stationary phase for chromatography or itself forms thestationary phase through its high specific surface area.

According to another advantage of the invention, the much smallerpressure drop through a multicapillary packing of equal characteristicdimension allows a strong increase in separating power.

The pressure drop of a particle bed follows Darcy's law. The pressuredrop of a multicapillary packing follows Poiseuille's law.

The pressure drop of a liquid phase (water at ambient temperature) for abed of particles of diameter 5 μm is 250 bar/m, and for capillaries ofdiameter 5 μm it is 18 bar/m at an eluting rate of 1 mm/s relative tothe total cross-section of the column. The void fraction of themulticapillary packing is assumed to be 0.7.

The pressure drop of a multicapillary packing of length 100 mm in thiscase is only 1.8 bar.

This in fact means that much narrower capillaries can be used and thatthe speed of analysis and efficacy can simultaneously be considerablyincreased in existing analytical chromatic equipment.

These different packing materials show linear dependence of pressuredrop on eluent velocity and length.

The separation impedance E is given by the formula:

E=t ₀ ·ΔP/(N²˜η)

For a particle packing, it is 2350.

For a multicapillary packing, it is 115.

A multicapillary packing is higher by two orders of magnitude in termsof impedance and separation. As mentioned previously, this means thatvery small capillaries can be used with high pressure pumps and theirperipherals and analysis speeds and efficacies can be increased by oneorder of magnitude.

For example, a multicapillary packing for HPLC can be proposed asfollows: in liquid phase for a given pressure drop, for a given numberof required theoretical plates, the diameter d_(c) at optimal efficacywill be written as follows for a single capillary:

d=(128·η·N·D/ΔP)^(1/2)

For a pressure drop of between 80 and 180 bars, and high efficacy of 100000 plates, the following equation can be drawn:

d _(c)=(0.84−1.46 μm

From a practical viewpoint, a packing for liquid phase analyticalchromatography may comprise a bundle of thousands of capillaries ofdiameter from 0.1 a 5 μm, and preferably a diameter of 0.1 to 1.5 μmseparated by walls having a thickness of 0.05 to 1.0 μm thickness inporous silica or alumina of high specific surface area.

Also, for gas chromatography, the channels are preferably given adiameter of more than 50 μm so as to maintain an acceptable pressuredrop.

The invention preferably concerns a packing for which the porous masshas a surface area of more than 20 m² per gram.

The diameters of the capillaries are preferably distributed following anormal law having a mean standard deviation of less than 0.5%.

The minimum elution time at optimal efficacy is 10 to 30 seconds for acolumn of length 100 mm, allowing very rapid and very efficient analysescompatible with the response times of existing detectors.

The packing allows a specific analysis speed of 3300 to 10000 plates persecond.

So that the feed rate is from 0.8 to 2.6 μl/mn, compatible with thepumping system developed for packed micro-columns, 3000 to 10000capillaries must be arranged in parallel. Higher feed rates can beensured by simply increasing the number of capillaries in parallel andthe cross-section of the packing.

For good efficacy of these structures, the homogeneity and regularity ofthe final packing must be as good as possible. The porosity of the wallsof the channels must be high, the void fraction best being 30 or 40% oreven higher. The thickness of the walls of the channels must be asnarrow as mechanically possible to increase the speeds of diffusionphenomena.

Also, the very low pressure drop of a multicapillary packing allows thepractical obtaining of devices which up until now have remained withoutany notable use.

A multicapillary packing can be seen as the assembly of a large numberof adjacent chromatographic columns.

The chromatographic packing allows the obtaining of a tool that is bothflexible and easy to use for performing preparative chromatography,continuous annular chromatography, in addition to conventionaltechniques of simulated mobile bed type.

A standard apparatus for continuous annular chromatography comprises:

-   -   an annular cylinder of multicapillary packing whose channels lie        parallel to its major axis. The two ends of this packing are        planar and perpendicular to its axis and act as support for the        fluid inlet and outlet assemblies.    -   Fluid inlet and outlet assemblies comprise separated angular        sectors which are fed with mixture to be separated or with        eluting solvent on the inlet side, and collect the different        eluted fractions on their outlet side. The walls delimiting the        feed and collecting sections are either in contact with the        packing via a seal sliding on the surface thereof, or they are        positioned very close to the cylindrical packing (within a few        micrometres for example) but not in contact therewith.

The inlet and outlet assemblies are fixed relative to one another for agiven separation at a given time.

The packing cylinder and the group formed by the inlet and outletassemblies move relative to one another in a movement of revolutionabout the axis of the packing cylinder.

This movement may be imposed upon the packing by a shaft to which it isattached. In this case the packing rotates in an outer ferrule machinedso as to leave slight play between the packing, or a protectioncontaining the same, and the ferrule under consideration.

Alternatively, it is the packing which is immobile and the inlet andoutlet assemblies are set in rotation.

The charging of the mixture to be separated and of the eluting fluid ismade through the different inlet sectors on the upstream side of thepacking.

The collection of the separated fractions is similarly performed onsectors of the downstream surface of the packing.

The constancy of residence time of each component in the packing allowsthe collection thereof at defined, constant, angular distances of theinlet sector.

The continuous feeding of the inlet sector, under these conditions,produces continuous collection of the separated components in the outletsectors.

The use of multicapillary packing materials in continuous annularchromatographs allows the lateral diffusion of the elution bands to beminimized to its pure diffusive component.

This is an important difference with devices formed of particle packingmaterials. This leads to an increase in separating power measured in NUTor NETP compared with particle packing materials of the prior art.

Without departing from the scope of the invention, the capillarychannels may be in the form of slits or bands.

In very similar fashion, it is possible to use the packaging materialsof the invention in continuous radial chromatography.

In this case, the multicapillary packing is conformed as a cylinder inwhich the capillary channels extend radially and not axially. Theiroperating principle is very close to that just described (see also FIGS.4, 5 and 6), the eluting fluid and the compounds to be separated in thiscase flowing inside the cylinder towards the outside of the cylinder, orvice versa. The feed and collecting sectors, in this case, are axialbands moving continuously relative to the annular cylindrical packing.

Continuous annular chromatography particularly allows the separation ofa large number of components having very close retention times, such asisomers, optical isomers, position isomers, etc. . . . in a single passin a single instrument, or in several passes in instruments placed incascade with or without intermediate re-concentration of the eluates.

The multicapillary packing materials of the invention can bemanufactured using any method known in the prior art and using the novelprocesses described below. The following processes are particularly welladapted.

One first process consists of covering and coating a bundle of fibreswith a solid matrix material and of destroying or removing the materialof the fibres so as only to leave the coating matrix subsisting throughwhich the capillary channels pass. The fibres are therefore theprecursors of the capillary channels.

The fibres can be removed by mechanical action, by fusion, vaporisation,dissolution, chemical attack, etc. . . .

Since the fibre acts as mould for the final capillary, very tightmanufacturing tolerances thereof allow very regular capillaries to beobtained down to micron sizes using well known monofilament productiontechniques, and therefore excellent performance levels of separation canbe reached. Submicron fibres exist. Nanometric fibres are in the courseof being developed. Schematically the aim is to prepare a compositematerial of which only the matrix is left to subsist.

A process according to the invention therefore comprises the steps ofjoining the precursor fibres of the capillary channels with a binder,thereby creating a matrix around the precursors, and removing the coreof the precursor fibres supporting the matrix by any means, oxidation,chemical attack, fusion and draining of the liquid, gasification so asto leave the matrix which can be used as base for chromatographicpacking.

One simple solution consists of assembling a bundle of hydrophilicfibres of the required diameter, immersing same in an aqueous solutionor suspension of a silica gel or alumina precursor solution whosepolymerization and/or the gel are ensured in situ.

In the present text, by <<silica gel precursor solution>> is meant aliquid of composition such that its development under the conditions ofthe manufacturing process leads to a silica gel. In particular, it maybe:

-   -   an acidified aqueous solution of an alkaline silicate,    -   an aqueous solution of an alkaline silicate whose metallic ions        have been absorbed and exchanged with H+ ions by an ion exchange        resin in its acid form,    -   a silica sol prepared by precipitation-growth of monomer or        weakly polymerized silica in a slightly basic aqueous phase on        nuclei to form spherical nanoparticles,    -   an aqueous solution at determined pH of an organometallic        molecule derived from silicon such as an alkoxysilane e.g.        tetraethoxyysilane, or tetramethoxyysilane.

Similarly, by <<alumina gel precursor solution>> is meant a liquid ofcomposition such that its development under the conditions of themanufacturing process leads to an alumina gel.

The small contact angle between the material of the fibre and thesolution promotes the creation of a film of homogeneous solution betweenthe fibres.

To form the capillary channels, the fibres are hydrolyzed in an acidmedium for example or carbonized and burnt.

Packing materials of porous silica and grafted porous silica can beobtained in this manner.

Packing materials of activated alumina can be obtained following thesame scheme.

For improved quality and homogeneity of the packing obtained, it may beuseful to start by coating the fibres with a jacket layer of a coatingmaterial called spacer material before assembling into a bundle.

It is possible that bare fibres may touch one another at contact pointsor lines and this will generate points of weakness and non-homogeneityin the packing.

In this case the process comprises coating a metal or non-metal fibrewith a thickness of adequate coating material called a spacer, thenjoining these fibres into bundle optionally with a binder, andselectively eliminating the material of the fibres by fusion,dissolution, vaporisation, chemical attack, etc.

In particular, the spacer may be porous and is partly or fullyintegrated in the final monolith.

The jacket or layer of spacer coating material can be deposited byco-extrusion of a core fibre with a polymer or a gel.

It can be deposited by immersing in a solution of a polymer, oroligomers subsequently treated by thermal polymerization or UV andcross-linking.

The jacket may be formed of a chemical deposit (metal, oxide), depositedby vapour phase, plasma spraying, vacuum evaporation, liquid phasedeposit. It can be deposited or sprayed using electric or electrostaticfields for non-conductive materials, the fibre being electrified to acertain potential, and a spacer powder being electrified to a potentialof opposite sign and placed close to the fibre so that it can bedeposited thereupon. It can be deposited by a printing technique ofinkjet type. It may be formed of an agglomerated powder or gel depositedby passing through a bath or liquid suspension.

The spacer may be formed of a powder deposited in a thin film from asuspension, or of any material able to be deposited in a film.

In particular, it may be made by immersing the fibre in a suspensioncontaining at least two constituents, first a powder mesoporous ormicroporous solid mineral, silica gel or activated alumina, and second amineral binder, silica or alumina sol respectively.

The first constituent carries the chromatographic separating functionand can be obtained by any known method, the function of the secondconstituent being to bind the solid particles mechanically togetherallowing handling of the coated film and its assembly into a bundle.

The binding action can be ensured by the sol gel, by drying, or by itsgelling followed by drying thereof.

Preferably, and so as not to clog the possible mesopores and microporesof the powder mineral solid, as mineral binder a sol is used whoseelementary particle size is greater than that of the mesopores.

It is possible in particular to ripen the sol under conditions causingits partial aggregation before mixing it with the mesoporous ormicroporous mineral solid.

For silica, this ripening can be conducted in a manner well known in thestate of the art by combining pH, temperature and ionic strength of thesol medium.

Finally, it is possible to use relatively dilute binder sols.

One or more organic texturing additives, or binders can be added to theimmersion suspension so as to impart sufficient mechanical strength tothe fibre for handling and shaping thereof.

These additives may form part of the final monolith or they may beremoved at a subsequent phase of the process.

The mechanical strength of the spacer can be ensured by sintering if thefibre withstands high temperatures (as is the case for iron or steelfibre for example).

The silica is used in its amorphous state.

For alumina, which exists in numerous crystallographic forms that aremore or less active and more or less crystallized, preferably aluminagels are used prepared from trihydrates (hydrargilite ou bayerite) ormonohydrates (boemite) activated by controlled calcining to a transitionalumina, in particular the aluminas γ, χ, κ, η or θ.

Preferably, the packing is made in a single allotropic variety ofalumina, so that all the sites behave in the same manner with respect tothe constituents of the mixture to be separated.

In particular, if the packing is composed of a powder deposited in anagglomerated suspension by a gel, it is desirable that the powder andgels should be activated to identical species after calcining.

Alternatively, in this same situation, it is possible to choose and tosynthesize the reinforcing gel so that its specific surface area afteractivation is small and negligible compared with that of the powderalumina.

Following another process, to avoid contact of the channel precursorfibres, these are assembled into a sheet by weaving.

If the precursor fibre is the warp, the weft fibre is used as spacer,and conversely.

The fibre perpendicular to the precursor may be a glass fibre, which hasgood thermal compatibility in terms of expansion coefficient with theporous mineral material of the monolith.

The chemical inertia of a glass fibre is excellent and comparable withthat of silica.

Since its specific surface is small it does not perturb analysis.

The fibres are assembled into a bundle and may be glued to each other.

The removal of the core of the fibres must be carried out so as not todestroy their matrix and/or their jacket layer. A choice can be madebetween several techniques, in particular:

-   -   By heating the assembly up to the melting temperature of the        core material of the fibres, and removing the liquid under a        pressure gradient. Easy melt metals such as tin, lead, bismuth,        antimony, the alloys thereof (so-called Newton, Darcet alloys,        etc.), or thermoplastic resins such as polyethylene,        polypropylene, PVC, etc. allow the operation to be conducted at        low temperature, from 70 to 200° C. for example. In this case,        the jacket or matrix and the material of the fibres must be as        compatible as possible in terms of thermal expansion, between        the manufacturing temperature and the melt temperature. This        method allows the core material to be recycled.    -   By forming fibres of a hydrolysable polymer, assembling the        fibres into a bundle and immersing the bundle in a precursor        solution of a mineral oxide, the solution being caused to gel        around the fibres, and eliminating the fibres by hydrolysis to        soluble species of low molecular weight. This manufacturing        process is also characterized in that the gel can be reinforced        by deposit via amorphous or crystalline growth of the mineral        oxide on the surface of its constituent particles to increase        its mechanical strength before drying.    -   If the spacer and the matrix are porous and allow the        impregnation or circulation of a reagent through the assembled        bundle, and contact thereof with the core material, its removal        can be achieved by dissolution, chemical reaction, in liquid or        vapour phase, etc. . . . This operation can be conducted at        moderate temperature, thereby avoiding problems of thermal        expansion. For example, it is possible to use the formation of        soluble or gaseous metallic chlorides, by direct action of the        chlorine on iron fibres or by thermal degradation of polymers to        their monomers as is the case with acrylic resins (PMMA), etc. .        . .    -   According to one variant of this method, the fibres are        assembled parallel to each other in a plane or sheet and        agglomerated with a porous or fibrous binder, or woven, so that        they are conformed into a thin sheet. A flexible sheet is        obtained by arranging the fibres of the binder perpendicular to        the channel precursors. Chemical attack of the core of the        channel precursor fibres can be performed via upper and lower        sides of the sheet. This sheet can then be chemically treated        etc. according to use and stacked or rolled in any arrangement.    -   The attack of the precursor fibre can be carried out from the        end faces of the packing, causing the reaction to advance        through inside the channels. Numerous processes can be used, in        particular when the reagent is a gas and the reaction product is        a porous solid not adhering to its substrate. For example, with        regard to iron fibres:

T=250° C. Fe+3/2Cl₂→FeCl₃(F=282° C., Eb=315° C.)

-   -   The difference between the gaseous chlorine pressure in        equilibrium with the metal and the pressure of operating        conditions applied at the fibre input enables the chlorine        permanently to reach the interface of the fibres and to be        consumed. The removal of the FeCl3 can be obtained by cyclic        evaporation, or under gravity with vibration. The removal of the        core of the fibres may take place over several steps of attack        and elimination of the formed product.

Among the hydrolysable polymers mention may be made inter alia of thepolyesters derived from glycolic acid, from lactic acid, from cellulose,and in particular polyglycolic acid or its copolymers with lactic acid,with ε-caprolactone or with trimethylene carbonate. Preferably, apolymer is chosen whose hydrolysis is rapid at a temperature of 80 to100° C.

According to an improvement of the invention, the channel precursorfibres comprise a sub-layer (sub-layer vis-à-vis the monolith, outerlayer vis-à-vis the core of the fibre) of a compound such as awater-soluble polymer, a hydrolysable polymer, a water-swelling polymer,or a wax or a metal melting at a temperature higher or slightly higherthan the temperature of the manufacturing process of the composite.

This sub-layer surrounds the core of the fibre.

This sub-layer is called an ablative layer in this document.

This ablative layer is made by deposit on the core of the fibre beforeforming the monolith preform.

This so-called ablative layer may be intermediate between the core ofthe fibre and the spacer.

An ablative layer of wax or metal melts into a liquid product of lowviscosity.

This pre-treatment has two advantages:

-   -   the expansion differential between the fibre and the matrix can        be offset for example by evacuating the liquid molten wax.    -   The disappearance, degradation or evacuation of the ablative        layer provides access to the core of a packing, optionally a        bulk packing, made from low cost fibres, polyolefins, cellulose        acetate, etc. . . . It is therefore possible to provide access        thereto for a reagent liquid (acid hydrolysis solution,        reinforcing nanosol etc. . . . ), or a drying gas.

Among the existing waxes it is possible, without this list beingexhaustive, to use: paraffins, fatty acids higher than C12, the estersof fatty acids such as the esters of glycerin, carnauba wax, aliphaticor aromatic waxes derived from the hydrocarbon industry.

The ablative layer may for example represent between 1% and 40% of thecross-section of the fibre coated with this sub-layer. The core of thefibre, in this case, may advantageously ensure the mechanical strengthof the filament

According to another embodiment of this manufacturing pathway, it ispossible to form the monolith separating the capillary channels using aprocess causing the formation of two families of pores, a family ofmesopores and a family of interconnected macropores such as described inthe publications by N, Ishizuka and Holloway R cited at the start ofthis description. This improvement provides major advantages:

The moist silica gel created by these processes around the channelprecursor fibres is highly permeable to fluids and in the moist stateallows the circulation through the packing mass of a liquid or gaspreferably through its inlet and outlet sides.

-   -   This circulating fluid inter alia can have the role of modifying        the porous structure of the bimodal gel and hence of the final        packing.    -   It may have the role of bringing a reagent into contact with the        fibre causing its elimination.    -   This elimination may be achieved using the previously described        methods, in particular by hydrolysis, dissolution or        gasification.    -   It may allow exchanging of mother liquors of the gel by an        organic fluid whose drying is less destructive for the gel        structure.    -   It may allow drying of the packing by circulating a gas or        supercritical fluid before eliminating the channel precursor        fibres.    -   The high porosity of the walls of the monolith obtained is        favourable for rapid completion of diffusion processes between        the channels.

The macropores may preferably represent a sufficient fraction of porousvolume of the solid mass of the monolith, sufficient to ensure thepercolation and interconnection thereof so as to allow the flow of afluid. Preferably, this fraction is higher than 40% and furtherpreferably higher than 70%.

It will be noted that at all events when the mass of the packing isformed of nanoscopic particles of agglomerated amorphous silica (silicagel) it can be reinforced before drying either by ripening at basic pH,or by depositing or precipitating amorphous silica thereupon in anaqueous phase so as achieve mechanical reinforcement by rigidifying itsstructure.

It is difficult to carry out precipitation of silica in a dense object,since the solubility of silica in water is very low (400 ppm at 100°C.). Permissible supersaturations of the order of 500 ppm, can onlyreinforce the outer layers of a bulk object since the weak diffusiveflow is instantly precipitated in contact with the high specific surfacearea of the packing. By bulk is meant herein the porous mass of themonolith.

One answer to this problem could be formulated as follows:

This deposit or precipitation can be performed by placing the gel inclose contact with nuclei or seeds of amorphous silica of very smalldiameter, from 2 to 4 nm for example, or nanosol, in concentratedsolution under conditions of low ionic strength (molar content of saltless than 0.1 to 0.15 N).

These nuclei, on account of their very small diameter and the effect ofsurface tension forces, are in equilibrium with a concentration ofsilica in aqueous pause that is greater than that in equilibrium withthe constituent silica particles of the packing of specific surface arealarger than 350 m²/g for example.

The solubility S of the particles of diameter d (Ralph K. Iler, Thechemistry of Silica, 1979, p 50) is written:

S/So=exp(4EV/R/T/d)

The surface tension E for silica is of the order of 46 erg/cm² (Ilerp54).

These nuclei may be created by acidification up to pH 9 of a dilutesolution of sodium silicate, either by an acid, or by an ion exchanger.These nanosols are sufficiently stable to exist for several tens ofminutes in solution, at notable concentrations for example 5 to 20 g/Iin silica equivalent.

Their contact and their circulation at 90-100° C. in very closeproximity with the walls of the capillaries allows the particles of thenanosol to diffuse via Brownian motion inside the constituent gel of themonolith down to major depths, of several hundred microns, and tore-dissolve thereat and deposit reinforcing silica at depth on thesurface of this constituent gel of the monolith.

The depth of penetration, i.e. of reinforcement of the gel depends uponthe diffusivity of the nanosol (between 0.5 and 1.0 10-9 m2/s, Einsteinequation)) and on the speed of kinetic phenomena ofredissolution-reprecipitation of the amorphous silica between thenanosol and the gel.

It is necessary to operate with nanosols and packing materialsimpregnated with an aqueous solution of low ionic strength and low basicpH (9 to 10), so as to avoid coalescence of the silica particles betweeneach other.

The driving force of the process is the much greater difference indriving concentration of diffusion allowed by the nanosol.

A silica packing can be hydrophobized or surface modified by a silanesuch as hexamethyl disilazane, silanes allowing coupling to C₈ or C₁₅straight carbon chains, or any other known silane, or any other methodfor treating a silica surface known in the state of the art.

A packing in alumina can be co-precipitated or impregnated withadditives, its acid-base status can be adjusted.

Without departing from the scope of the invention, the channel precursorfibre may be formed of a capillary tube, a fibre of various geometriccross-sections (square, hexagonal, etc).

Without departing from the scope of the invention the channel precursorfibre may itself be porous.

Another process for manufacturing the monolithic material comprises theforming and assembling of thin films. This process uses as base materialthin films or sheets of material. This material may be a precursor ofamorphous silica, such as a silicon resin.

The process can be implemented by printing channels via etching,photo-etching, drawing or moulding in a sheet of silicone elastomer, andstacking or rolling of the sheets into the shape of the desired finalpacking. Subsequent treatment by pyrolysis and oxidation transforms thesilicon to amorphous silica crossed by free channels.

In this case, a multicapillary packing is prepared by the assembly of alarge number of multicapillary packing elements.

FIG. 1 is a cross-sectional view of cylindrical multicapillary packingfor chromatography according to the invention, following a directionperpendicular to its major axis.

It comprises a porous mass of amorphous silica 2 and void capillarychannels 1 in which the fluid passing through the packing 3 is able tocirculate freely.

In the described case, the capillary channels are straight, parallel andregularly spaced. The different channels have morphologies and diametersthat are as identical as possible. Each channel passes through themonolithic material i.e. its ends are open on each side 4 and 5 of thecylindrical packing, allowing the circulation of the fluid from theinlet side towards the outlet side.

Said material can therefore be used in a chromatographic column.

FIG. 2 is an overhead view of one side 5 of the cylindrical packing seenalong direction 6. The openings of individual capillary channels 1 canbe seen in the porous mass 2.

FIG. 3 is a cross-sectional view of a film of a silicone elastomer 40 inwhich transverse channels 41 are arranged that are parallel andperpendicular to the plane of the figure, whose stacking or rolling intocylinder shape about an axis parallel to the channels forms a preform ofthe final packing.

The preform is then heated and oxidized to obtain the multicapillarypacking of amorphous silica with high specific surface area.

FIGS. 4, 5 and 6 are block diagrams of a continuous annularchromatograph using a multicapillary packing for the separation of twoproducts. Diagram 4 is a cross-section of the instrument along AA′.Diagram 5 is a cross-section of the instrument along BB′ (i.e. theupstream part of the chromatograph), diagram 6 is a cross-section of theinstrument along CC′ (i.e. its downstream part).

Said annular chromatograph comprises a cylinder of multicapillarypacking 7 whose capillary channels are parallel to its major axis. Itstwo sides 13 and 16 act as support for the fluid inlet and outletassemblies. A representative part of the packing 7 can be seen incross-section in FIG. 5.

This instrument further comprises fluid inlet 9, 22, and outletassemblies 17, 25, 24 and 23 which are in the form of angular sectorsseparated by vertical walls which slide over the packing by means offlexible seals without damaging the packing, or are positioned veryclose thereto i.e. a few microns or tens of microns away without anydirect contact and therefore without any wear part, imparting the sealor the plate separating two sectors with sufficient thickness so thatthe leak flow rate caused by play is smaller than the flow evacuatedtowards the downstream side by the fraction of packing lying under theseal.

Owing to the low pressure drop of the multicapillary packing, therelative pressure differences between the different feed sectors of thechromatograph may be relatively high and hence easily adjusted It iseffectively easier to adjust a pressure difference of 0.03 bar betweentwo chambers brought to 0.3 bars relative (relative to the atmosphere)than the same pressure difference between two chambers brought to 3 bars(relative). The leak flow rate of the feed and eluting fluids betweenthe different sectors is directly proportional to the square root of thedifference in pressure between these sectors, and not to the absolutepressure prevailing therein.

For precise adjustment of this distance, the packing is sealed to anexternal cylinder which may be in a machined material for example.

The inlet and outlet assemblies are fixed relative to one another.

Each sector on the inlet and outlet sides is connected to an inlet port10, 12 and outlet port 21.

The cylindrical packing and its inlet and outlet assemblies moverelative to one another in a circular movement 18 about the axis OO′.This movement is imposed upon the packing by a drive shaft 19 via acentral shaft 11 to which the packing is attached.

The packing rotates inside a ferrule 15, 20 closely adjusted to itsouter diameter. The feeding of the mixture to be separated via port 10and of the eluting fluid via port 12 takes place through differentsectors 9 and 22 of its upstream surface, and the collection of thedifferent eluted fractions similarly takes place on different sectors ofits downstream surface (sectors 17 and 24 for the two separatedcomponents and 23 and 21 for the eluent).

The constancy of residence time for each component in the packing allowsthe collection thereof at determined angular distances of the feedsector. The continuous flow in the feed sectors in this case produces acontinuous production flow in the outlet sectors.

FIG. 7 is a schematic cross-sectional view of a radial multicapillarypacking 30 in which the channels 31 extend radially from inside thepacking towards its periphery, separated by walls 32.

FIG. 8 is a radial view of a constituent element of the same packing. Inthis case, the packing is formed of a coaxial stack of discs 30 so as tocreate the conduits for forming capillary channels.

The continuous annular chromatographs just described lend themselvesparticularly well to gas chromatography, the vector gas able to becooled and recycled or continuously re-circulated by means of low-costapparatus such as fans, without requiring compressors to be included inthe circuit.

In addition, the continuity of the flows avoids the need for gas valveswith sequential opening as required by discontinuous industrialinstallations.

Finally, the low absolute pressures conveyed allow sealed functioningand easy adjustment of the assembly.

EXAMPLES

Different modes are described below for preparing capillary channels inthe monolithic porous material of the invention.

Example 1 Preparation of a Multicapillary Packing in Silica Using a SolGel Process

In this embodiment the fibres are formed of a hydrolysable polymer andare assembled into a bundle. The bundle is immersed in a silica gelprecursor solution, a solution which is caused to gel around the fibres;the fibres are then eliminated by hydrolysis to soluble species of lowmolecular weight.

A Caprosyn Tyco Healthcare monofilament, grade 5 (outer diameter ofabout 150 μm) is immersed in an aqueous solution containing 10% of apolyvinyl alcohol and 15% by weight of glass micro-beads of diameterbetween 0 and 40 μm supplied by Potters Ballotini. The monofilament isthen dried. In this manner the outside of the Caprosyn filament iscoated with glass micro-beads which act as spacers adhering to itssurface through the action of the PVA which acts as adhesive.

A bundle is fabricated by assembling 9 of these fibres laterallytogether in a rectangular section with sides of 2000 μm by 250 μm andlength of 20 mm. The bundle is formed in a rectangular channel of theabove-mentioned dimensions, the depth being 250 μm, hollowed out of aTeflon sheet 20 mm×20 mm×10 mm.

The bundle of Caprosyn fibres is impregnated with a mixture of LudoxTM50 (Grace trademark, sol of amorphous silica particles 22 nm indiameter, having a specific surface area of 140 m2/g, containing 50% byweight of silica) and 98% sulfuric acid in adequate proportions toobtain a 10% by weight solution of sulfuric acid relative to the water.The liquid must fill the entirety of the packing, which must be immersedtherein. The packing is closed with an upper planar sheet, or cover, ofTeflon of identical dimensions to the previous sheet, screwed thereupon.

The assembly is brought to 100° in a hot water bath.

The sol gels very rapidly under these conditions, in 10 mn to one hour.It produces a non-reinforced packing moulded around the fibres.

Each end of the bundle projecting beyond the Teflon sheets is cut with avery fine blade to release the channel section.

The device is left to react 48 hours at the temperature of 100° C. todissolve the fibres by hydrolysis.

The packing is then opened by removing the cover.

A second cover in Teflon of identical outer dimensions to the previouscover comprising and allowing a free channel 3 mm thick and 5 mm wide tobe provided above the packing is positioned and centred above the lengthof the channels and joined to the base carrying the same. This coverallows the circulation of a gas flow and contact thereof with the entirelength of the channels.

The assembly is brought to 112° C. and a flow of steam at 0.5 ml/s ismaintained through the free channel purging for 24 hours.

The temperature is then brought to 180° C. for 12 hours under the samesteam purging.

The temperature is finally brought to 250° C. for 12 hours, under thesame steam purging, then the packing is cooled to ambient temperature.

The upper cover is then detached and the packing released.

FIG. 9 is a photograph of a cut made in a packing 3 obtained using themethod just described.

As can be seen, the channels 1 surrounded by porous silica 2 are regularand uniform.

Example 2 Preparation of a Multicapillary Packing in Silica Using a SolGel Process

In this embodiment, the fibres are formed of a hydrolysable polymer,assembled into a bundle. The bundle is immersed in a silica gelprecursor solution, the solution then being caused to gel around thefibres and the fibres are eliminated by hydrolysis to soluble species oflow molecular weight. This fabrication method also comprisesreinforcement of the silica gel by depositing silica on the surface ofits constituent particles before drying.

A Caprosyn Tyco Healthcare monofilament, grade 5 (outer diameter ofabout 150 μm) is immersed in an aqueous solution containing 10% of apolyvinyl alcohol and 15% by weight of glass micro-beads of diameterbetween 0 and 40 μm supplied by Potters Ballotini. The monofilament isthen dried. In this manner, the outside of the Caprosyn filament iscoated with glass micro-beads which act as spacers adhering to itssurface via the action of the PVA which acts as adhesive.

A bundle is made by assembling 7 of these fibres in a rectangularsection of sides 1700 μm by 250 μm and length of 100 mm. The bundleformed in a square channel of the above-mentioned dimensions, the depthbeing 250 μm, hollowed out of a sheet of 316L stainless steel 100 mm×20mm×10 mm, or module.

On a planar face of the Teflon cover of the module, a solution ofpolyglycolic acid or polyglycolide in hexafluoroisopropanol (HFIP) isdeposited so as to leave on this face after drying a thickness ofpolyglycolide of about 5 micrometres.

The bundle of Caprosyn fibres is impregnated with a mixture of LudoxTM50 (Grace trademark, sol of amorphous silica particles 22 nm indiameter, and specific surface area of 140 m2/g, containing 50% byweight of silica) and 98% sulfuric acid in adequate proportions toobtain a 10% by weight solution of sulfuric acid relative to the water.The liquid must fill the entirety of the packing which must be immersedtherein. The packing is closed by an upper planar sheet of Teflon, orcover, of identical dimensions to the previous sheet, screwed thereuponthe side coated with polyglycolide against the packing.

The assembly is brought to 100° C. in a hot water bath.

The sol gels very rapidly under these conditions, in 10 mn to one hour.It produces a non-reinforced packing moulded around the fibres.

The device is left to react for 24 hours.

Each end of the bundle projecting beyond the Teflon sheets is cut with avery fine blade to release the section of the channels.

After this operation, the cover is removed releasing the upper surfaceof the gel.

This operation and the washings are performed by maintaining thenon-reinforced packing immersed in its liquid treatment bath betweeneach step, and limiting nearby turbulence inasmuch as possible.

The device is left to react 7 hours at the temperature of 100° C.immersed in a bath of 16% sulfuric acid in water so as to complete thedissolution of the fibres by hydrolysis.

The packing is washed with two consecutive five-hour strippingoperations with one litre of demineralised water at 100° C. previouslysaturated with amorphous silica, then with a buffer solution diluted topH 9 at 100° C. for five hours, then with three consecutive five-hourstripping operations with one litre of demineralised water at 100° C.previously saturated with amorphous silica.

A second cover in Teflon of outer dimensions identical to the packingsupport, comprising and allowing a free channel 0.25 mm thick and 1.7 mmwide to be provided above the packing is positioned and centred over thelength of the channels and joined to the base carrying the same. Thiscover allows the circulation of a flow of liquid and contacting thereofwith the entire length of the channels.

This upper channel is fed via one of its ends with an aqueous suspensioncontaining 1.4% silica sol with very high specific surface area (1000 to1700 m2/g) stabilized at pH9. This solution or aqueous suspension isobtained by mixing a 0.4 M solution of boric acid with sodium silicatein concentrated solution of density 1.34 so as to obtain a 0.15 Msolution of sodium ions that is used immediately. The feed is maintainedat a temperature of 100° C. so that the entire wet part of the immersionprocess of the fibre until reinforcement of the gel is conducted at aconstant temperature of 100° C. In this manner it is possible to ensureperfect morphology of the packing. The reinforcing mechanism is Oswaldripening, the smallest particles dissolving whilst the largest grow indiameter owing to the greater solubility of the silica in equilibriumwith particles of narrow diameter. The flow is maintained at a velocityof 3 cubic millimetres/s. The reinforcement lasts 60 mn.

The packing is then washed with a dilute aqueous solution of sulfuricacid at pH2, then with demineralised water. The cover is removed and thepacking is rapidly dried under a direct steam of dry air at 105° C.,then brought to 400° C. in air for one hour.

A cover is replaced on the packing. This cover has the same dimensionsas the previous cover but is made in 316L stainless steel.

The packing can be hot-rehydrated in an acid or basic aqueous solutionusing any known technique.

The packing can be used as such for chromatography.

It can be hydrophobized or surface modified with a silane such ashexamethyl disilazane or any other known silane, or any other method.

Example 3 Preparation of a Multicapillary Packing in Silica Using a SolGel Process

In this embodiment, the fibres are formed of a hydrolysable polymer,assembled in a bundle. The bundle is immersed in a silica gel precursorsolution, a solution which is caused to gel around the fibres, and thenthe fibres are eliminated by hydrolysis to soluble species of lowmolecular weight. This manufacturing process may also comprisereinforcing of the silica gel by depositing silica on the surface of itsconstituent particles before drying.

A Caprosyn Tyco Healthcare monofilament, grade 5 (outer diameter ofabout 150 μm) is immersed in an aqueous solution containing 10% of apolyvinyl alcohol and 15% by weight of glass micro-beads of diameterbetween 0 and 40 μm supplied by Potters Ballotini. The monofilament isthen dried. In this manner, the outside of the Caprosyn filament iscoated with glass micro-beads which act as spacers adhering to itssurface via the action of the PVA which acts as adhesive.

A bundle is manufactured by assembling 49 of these fibres in a squaresection with sides of 1700 μm and length of 100 mm. The bundle isassembled within a square channel of the above-mentioned dimensions(square section) hollowed out of a 316 L stainless steel sheet 100 mm×20mm×10 mm.

On one side of the Teflon cover of the module, a solution ofpolyglycolic acid or polyglycolide in hexafluoroisopropanol (HFIP) isdeposited so as to leave on this side after drying a thickness ofpolyglycolide of about 5 micrometres.

The bundle of Caprosyn fibres is impregnated with a mixture of LudoxTM50 (Grace trademark, sol of amorphous silica particles 22 nm indiameter, specific surface area of 140 m2/g, containing 50% by weight ofsilica) and 98% sulfuric acid in adequate proportions to obtain a 10% byweight solution of sulfuric acid relative to the water. The liquid mustfill the entirety of the packing which must be immersed therein. Thepacking is closed with an upper planer sheet, or cover, of Teflon ofidentical dimension to the previous sheet, screwed thereupon the sidecoated with the polyglycolide against the packing.

The assembly is brought to 100° C. in a hot water bath.

The sol gels very rapidly under these conditions, in 10 mn to one hour.It produces a non-reinforced packing moulded around the fibres. Thedevice is left to react for 12 hours.

Each end of the bundle projecting beyond the Teflon sheet is cut with avery fine blade to release the section of the channels.

After this operation, the cover is removed releasing the upper surfaceof the gel.

This operation and the washings are performed maintaining thenon-reinforced packing immersed in its liquid treatment bath betweeneach step, limiting nearby turbulence inasmuch as possible.

The device is left to react 24 hours at the temperature of 100° C.immersed in a bath of 16% sulphuric acid in water to dissolve the fibresby hydrolysis.

This treatment is completed by immersion in 40% nitric acid at 100° C.for five hours.

The packing is washed with two consecutive five-hour strippingoperations in one litre of demineralised water at 100° C. previouslysaturated with amorphous silica, then with a dilute buffer solutiondiluted to pH9 at 100° C. for five hours, then with three consecutivefive-hour stripping operations with one litre of demineralised water at100° C. previously saturated with a amorphous silica.

A planar cover is replaced over the packing. This cover has the samedimensions as the first but is made in 316L stainless steel.

The silica of the packing at this stage ill resists drying on account ofthe weak bonds between the individual gel particles. To increase theforce of this bonding, silica is deposited around the particles andparticularly around their point of contact in sufficient quantity.

For this use, the packing is fed via one of its ends with a 1.4% aqueoussolution of silica sol with very high specific surface area (1000 to1700 m2/g) stabilized at pH9. This solution or aqueous suspension can beobtained by mixing a 0.4 M boric acid solution with sodium silicate inconcentrated solution of density 1.34 to obtain a 0.15 M solution ofsodium ions that is used immediately. The feed is maintained at atemperature of 100° C. The flow is maintained at a velocity of 7 cubicmillimetres/s for the packing. The reinforcement lasts 60 mn.

The packing is then washed with a dilute aqueous solution of sulfuricacid at pH 2, followed by washing with distilled water, to eliminate allthe impurities and basicity of the packing. It is then dried in a streamof dry hot air at a temperature of 120° C.

The packing can be used as such for material exchange.

It can be activated by pyrolysis.

It can be hydrophobized or surface modified with a silane such ashexamethyl disilazane or any other known silane, or any other method.

Example 4 Preparation of a Multicapillary Packing in Polymer and PorousCarbon

The present example is given by way of indication to evidence the greatease of use and flexibility of application of the process according tothe invention to prepare monoliths having rectilinear capillary channelsparallel to one another and intended for chromatography.

The starting material is a wire in a tin and lead alloy in proportionsof 60%, 40% respectively. Its diameter is 7/10 mm. The wire is cut intorectilinear needles 15 cm in diameter coated with a thin layer byimmersing in a mixture of a non-polymerized epoxy resin and powdersilica in suspension in tetrahydrofuran (20% araldite, 80% THF, and avolume of Aerosil 380 equivalent to ¾ of the volume of the solution).The needles are placed 24 hours close to a heat source (50° C.). Theyare then cut into lengths of 100 mm and assembled in a bundle ofdiameter about 14 mm in a glass tube of length 80 mm and inner diameterof 18 mm that is previously prepared.

The inner wall of this tube is previously coated, before insertion thebundle, with a layer of polyester of thickness about 2 mm, polymerizedin situ.

A liquid polyester resin and its polymerization activator are thenpoured into the tube via the interstices of the needles so as to fillthis void space completely. The resin is polymerized for 24 hours atambient temperature.

The composite thus formed is released by sectioning the needles over alength of 10 mm either side of the glass tube, flush with its ends andperpendicular to the needles.

The bundle is immersed in an oil bath at 190° C. until melting of theneedles and the molten metal is easily eliminated via light circulationof pressurized air.

Example 5

In this variant, polymeric fibres precursors of the channels areassembled in a bundle, the bundle is immersed in a silica gel precursorsolution, this solution being caused to gel around the fibres, then thefibres are eliminated by pyrolysis and combustion. The silica gel can bereinforced by depositing silica on the surface of its constituentparticles before dying.

A Nylon monofilament (outer diameter of about 150 μm) is immersed in anaqueous solution containing 10% of a polyvinyl alcohol and 15% by weightof glass micro-beads of diameter between 0 and 40 μm supplied by PottersBallotini. The monofilament is then dried. In this manner, the outsideof the filament is coated with glass micro-beads which act as spacersadhering to its surface via the action of the PVA which acts asadhesive.

A bundle is fabricated by assembling these filaments into a bundle ofrectangular section, 1700 μm in width, 250 μm in depth and 100 mm inlength. This bundle is created by rolling inside a said channelprecisely machined in a sheet of 316L stainless steel 100 mm×20 mm×10mm. This bundle of polyester fibres is impregnated with a mixture of24.3 g of tetramethylsiloxane, and 57.6 ml of a 1% ammonia solution inwater. The liquid must fully wet and fill the packing.

The packing is closed with an upper cover formed of a planar sheet ofstainless steel of identical dimensions to those of the base stainlesssteel sheet, screwed thereupon, on which a thickness of about 5micrometres of paraffin melting at 62° C. has previously been deposited.

The mixture is left to polymerize and gel for 24 hours at 42° C.

The two ends of the packing are cut flush with the steel sheet torelease the section of packing.

The packing has a length of 100 mm.

The packing and its jacket are brought to 90° C.

The cover is removed and the packing is dried in dry air at atemperature of 105° C. for 2 hours.

The resulting product is heated to 650° C. in an atmosphere of air at arate of 100° C. per hour starting from ambient temperature, forconversion thereof to a multicapillary packing by burning the polymericfibres.

Once cooled, the packing is again closed on its upper part by a planarsheet of stainless steel, or cover, of same dimensions screwed onto theone containing the packing.

Example 6

A wire of a mixture of Pb, Sn, Bi in weight proportions of 32, 15, 53melting at 96° C., is produced with a diameter of 0.5 mm.

This wire is cut into rectilinear needles of length 120 mm.

200 g of Silica Gel for chromatography (Acros reference 24167) is grounddown to a mean particle size of about 10 μm.

The powder is gradually placed in suspension 500 ml of a mixture of 200ml of silica sol TM50 by Grace containing 50% dry matter, and 300 ml ofdemineralised water maintaining the pH at 9.5 with a continuous supplyof sodium hydroxide N.

1.0% of a 10% solution of perfluoroctane sulfonate is added.

Once the placing in suspension is completed, the metal wire is immersedin the suspension of silica held under agitation. It is suspended in aflow of moist air at 80° C. saturated by passing in a 10% solution ofacetic acid in water for 1 h so that the sol gels without evaporating.It is then instantly dried under a stream of dry air at 80° C.

The needles are then cut to an exact length of e 100 mm clearing eachside, and they are arranged in a hexagonal housing of sides 2.6 mm andlength of 100 mm formed of two semi-shells hollowed out of a 316Lstainless steel sheet 20×10×100 mm. The needles are arranged parallel toeach other and regularly in seven successive layers on the lowersemi-shell.

The two semi-shells are screwed onto each other.

A mixture is prepared of Ludox TM50 (Grace trademark, sol of amorphoussilica particles, 22 nm in diameter, specific surface area of 140 m²/g,containing 50 weight % silica) and of 98% sulphuric acid in adequateproportions to obtain a 5% sulfuric acid solution relative to thecontained water.

The bundle of metallic needles is impregnated with this mixture. Theliquid must fill the entirety of the packing which must be immersedtherein.

The mixture is held at 90° C. until complete gelling of the sol.

The steel shell containing the bundle is extracted from the gel, itsends are released and it is arranged vertically in a boiling hot waterbath at 100° C. The metal melts and flows naturally out of the bottom ofthe bath releasing the capillary channels.

The monolith is washed with deionized water percolated through the freechannels.

The monolith thus obtained can be used directly for aqueous phase liquidchromatography.

It can be activated by pyrolysis.

It can be hydrophobized or surface modified with a silane such ashexamethyl disilazane or any other known silane, or any other method.

Example 7

A wire of a mixture of Pb, Sn, Bi in weight proportions of 32, 15, 53melting at 96° C., is produced with a diameter of 0.5 mm.

This wire is cut into rectilinear needles of length 120 mm.

These needles are immersed in a solution in water of 0.5% polyvinylalcohol containing 0.05% of surfactant FC-4430 by 3M, and dried at atemperature of 80° C.

200 g of activated alumina neutral for chromatography (Acros reference19041) is ground down to a mean particle size of about 10 μm.

An alumina sol is prepared in the following manner.

About 700 g of non-hydrated aluminium nitrate (Al(NO3)3, 9 H2O) foranalysis—Acros) are dissolved in one litre of deionized water at 22° C.under agitation until saturation. 1520 g of urea are added to themixture and solubilized.

The solution is held at 22° C. for one hour and passed through a 0.22 μMMilllipore filter.

The solution obtained is held at 90° C. for 12 hours.

The alumina powder is gradually placed in suspension in 500 ml of thisalumina sol maintaining the pH of the solution constant by adding 0.1Nammonia solution.

Once the placing in suspension is completed, the metal wire is immersedin the suspension of alumina held under agitation. It is then instantlyplaced and suspended in a confined atmosphere, to avoid any earlydehydration, at 90° C. until the sol gels. It is then dried in a streamof dry air at 80° C.

The needles are then cut into exact lengths of 100 mm clearing eitherside and are arranged in a hexagonal housing of sides 2.6 mm and lengthof 100 mm formed of two semi-shells hollowed out of a 316L stainlesssteel sheet 20×10×100 mm.

The needles are arranged parallel to each other and regularly in sevensuccessive layers.

The two semi-shells are screwed onto each other.

A second alumina sol is prepared in the same manner as previouslymentioned in this example.

The bundle of metallic needles is impregnated with this sol inserted viathe interstices of its free ends. The liquid must fill the entirety ofthe pacing which must be immersed therein.

The mixture is held at 90° C. until complete gelling of the sol.

The steel shell containing the bundle is extracted from the gel, itsends are freed and it is arranged vertically in a boiling hot water bathat 100° C. The metal melts and flows naturally to the bottom of the bathreleasing the capillary channels in an alumina packing of high specificsurface area.

The monolith is washed with deionized water percolated through the freechannels

The monolith can later be dried and activated at a temperature of 250 to650° C.

It will be noted that in all the examples provided above, thepercentages are weight percentages.

1. A monolithic porous material based on amorphous silica or activatedalumina, comprising substantially rectilinear capillary channelsparallel to one another, wherein: the channels have a substantiallyuniform cross-section relative to each other, the cross-section of eachchannel is regular over its entire length, the channels pass through thematerial from end to end, the length of the channels is equal to or morethan 10 mm.
 2. The material of claim 1, wherein the standard deviationof the diameter of the channels is less than 30% of the diameter,preferably less than 5% thereof.
 3. The material claim 1, having arelative volume of capillary channels that is less than 90%.
 4. Thematerial of claim 1, wherein the thickness of the wall between twoadjacent channels, in its narrowest part, is less than one half of theirdiameter.
 5. The material of claim 1, wherein the capillary channelshave a diameter of between 0.1 and 1.5 micrometer.
 6. The material ofclaim 1, wherein the capillary channels have a diameter greater than 50μm.
 7. The material of claim 1, formed of amorphous silicasurface-modified by a silane.
 8. The material of claim 1, based on analumina γ, χ, κ, η or θ.
 9. A chromatographic column whose packingcomprises at least one monolithic porous material according to claim 1.10. An axial, continuous annular chromatographic apparatus wherein thepacking comprises at least one monolithic porous material according toclaim
 1. 11. A radial, continuous annular chromatographic apparatuswherein the packing comprises at least one monolithic porous materialaccording to claim
 1. 12. A process for preparing a monolithic porousmaterial based on amorphous silica or activated alumina comprisingsubstantially rectilinear capillary channels parallel to one another,comprising the steps of: providing a bundle of so-called channelprecursor fibres whose diameter is equal to the diameter of thecapillary channels, forming a porous matrix of amorphous silica oractivated alumina around the fibres, eliminating the fibres so as toform said capillary channels in said matrix.
 13. The process of claim12, wherein the channel precursor fibres comprise an ablative layer of acoating material that is removed during a first fibre eliminationtreatment step.
 14. The process of claim 12, wherein the channelprecursor fibres are coated with a spacer before forming the bundle toensure a minimum thickness of monolith between two adjacent channels.15. The process of claim 12, wherein the porous matrix of amorphoussilica has a high proportion of macropores allowing the circulation of afluid in the monolith.
 16. The process of claim 12, wherein the fibresare formed of a hydrolysable polymer, in that the fibres are assembledin a bundle, in that the bundle is immersed in a silica gel precursorsolution, the solution being caused to gel around the fibres, and inthat the fibres are eliminated by hydrolysis to soluble species of lowmolecular weight.
 17. The process claim 12, wherein the channelprecursor fibres are metal wires with low melting point coated with afilm of silica or activated alumina, assembled in a bundle, in that thebundle is immersed in a silica gel or activated alumina precursorsolution, the solution being caused to gel around the fibres, and inthat the fibres are eliminated by melting and draining the molten liquidoutside the material.
 18. The process of claim 12, wherein the materialis amorphous silica, and in that this amorphous silica is reinforced bydepositing silica on the surface of its constituent particles, beforedrying thereof.
 19. A process for preparing a monolithic porous materialof amorphous silica comprising substantially rectilinear capillarychannels parallel to one another, comprising the steps of: formingconduits in at least one sheet of a silicone elastomer, stacking orrolling this or these sheets so as to close the conduits to formcapillary channels, pyrolysis and oxidation of the silicone to amorphoussilica.